Prevent style drift: pre-commit hooks + staged-file formatting/lint #9

Problem

Style regressions are reaching PR stage instead of being caught before commit.

Proposal

Introduce local guardrails:

• Pre-commit hooks (e.g. Husky + lint-staged)
• Run fast checks on staged files only
• Auto-fix where safe (prettier, phpcbf) before commit

Keep CI as strict backstop while local checks stay fast.

Acceptance criteria

• Pre-commit hook setup added.
• Staged-file lint/format commands added.
• Contributor docs updated with hook install/usage.